In general, depending on working conditions, an optional device, such as a breaker, may be mounted after a bucket of an excavator is carried off, and a combined work may be done through simultaneous driving of the optional device and an attachment. In this case, due to a difference in load pressure between the optional device and the attachment, hydraulic fluid may not be smoothly supplied from a hydraulic pump to the optional device and the attachment. Accordingly, by limiting the amount of hydraulic fluid that is supplied from the hydraulic pump to the optional device through a priority function, movement of the attachment can be prevented from being limited.
A priority function control apparatus for a construction machine in the related art, as illustrated in FIG. 1, includes a variable displacement hydraulic pump (hereinafter referred to as “hydraulic pump”) 1 connected to an engine, an optional device and an attachment (not illustrated) connected to the hydraulic pump 1, an optional device operation lever 2 and an attachment operation lever 3 outputting operation signals that correspond to their amounts of operation when an operator operates them, an optional device spool 4 installed in a flow path between the hydraulic pump 1 and the optional device and shifted to control a flow direction of hydraulic fluid that is supplied to the optional device in response to an operation of the optional device operation lever 2, and an attachment spool 5 installed in a flow path between the hydraulic pump 1 and the attachment and shifted to control a start, a stop, and a direction change of the attachment in response to an operation of the attachment operation lever 3.
As illustrated in FIG. 1, in the case where a combined work is done by driving the optional device and the attachment, which share the hydraulic pump 1, through operation of the optional device operation lever 2 and the attachment operation lever 3, the hydraulic fluid may not be smoothly supplied from the hydraulic pump 1 due to the difference in load pressure between the optional device and the attachment. That is, if the load pressure that is generated in the optional device is relatively lower than the load pressure that is generated in the attachment, the amount of hydraulic fluid that is supplied from the hydraulic pump 1 to the optional device is increased according to the hydraulic characteristics, and thus the movement of the attachment may be limited.
Accordingly, an orifice 6 is installed in a flow path between the hydraulic pump 1 and the optional device spool 4 so as to limit the amount of hydraulic fluid that is supplied to the optional device during the combined work in which the optional device and the attachment are simultaneously driven.
Another priority function control apparatus for a construction machine in the related art, as illustrated in FIG. 2, includes a variable displacement hydraulic pump (hereinafter referred to as “hydraulic pump”) 1 connected to an engine, an optional device and an attachment (not illustrated) connected to the hydraulic pump 1, an optional device operation lever 2 and an attachment operation lever 3 outputting operation signals that correspond to their amounts of operation when an operator operates them, an optional device spool 4 installed in a flow path between the hydraulic pump 1 and the optional device and shifted to control a flow direction of hydraulic fluid that is supplied to the optional device in response to an operation of the optional device operation lever 2, an attachment spool 5 installed in a flow path between the hydraulic pump 1 and the attachment and shifted to control a start, a stop, and a direction change of the attachment in response to an operation of the attachment operation lever 3, and a hydraulic pressure reducing valve 7 installed in a signal path between the optional device operation lever 2 and the optional device spool 4 and shifted to control signal pressure that is input from the optional device operation lever 2 to the optional device spool 4 in response to signal pressure from an outside.
Accordingly, in the case where a combined work is done by driving the optional device and the attachment through operation of the optional device operation lever 2 and the attachment operation lever 3, the amount of hydraulic fluid that is supplied to the optional device by the hydraulic reducing valve 7 is limited, and thus the movement of the attachment can be prevented from being limited.
However, as illustrated in FIGS. 1 and 2, in the case where the amount of hydraulic fluid that is supplied to the optional device by the orifice 6 and the hydraulic reducing valve 7, it may be difficult to smoothly adjust the extent of the priority function in accordance with the load conditions of the optional device. Further, an interface through which an operator can easily set the priority function is not provided, and in the case where the load conditions of the optional device are varied, it may be difficult to easily cope with such variation.
Still another priority function control apparatus for a construction machine in the related art, as illustrated in FIG. 3, includes a variable displacement hydraulic pump (hereinafter referred to as “hydraulic pump”) 1 and a pilot pump 8 connected to an engine, an optional device and an attachment (not illustrated) connected to the hydraulic pump 1, an attachment operation lever 3 outputting an operation signal that corresponds to the operation amount when an operator operates the attachment operation lever 3, an optional device spool 4 installed in a flow path between the hydraulic pump 1 and the optional device and shifted to control a flow direction of hydraulic fluid that is supplied to the optional device, an attachment spool 5 installed in a flow path between the hydraulic pump 1 and the attachment and shifted to control a start, a stop, and a direction change of the attachment in response to an operation of the attachment operation lever 3, an electrical operation device 9 for the optional device outputting an operation signal in accordance with an operator's operation to control the optional device, an electro proportional pressure reducing valve 10 installed in a signal path between the pilot pump 8 and the optional device spool 4 and shifted to convert signal pressure from the pilot pump 8 into secondary signal pressure so as to correspond to an electrical control signal from an outside and to supply the secondary signal pressure to the optional device spool 4, and a controller 11 outputting the electrical control signal that corresponds to the operation signal of the electrical operation device 9 for the optional device to the electro proportional pressure reducing valve 10.
Accordingly, in the case where the electrical operation device 9 for the optional device and the attachment operation lever 3 are operated, the operation signal that is generated in accordance with the operation of the electrical operation device 9 for the optional device is input to the controller. In accordance with the electrical control signal that is output from the controller 11 to correspond to the operation signal, the electro proportional pressure reducing valve 10 generates the secondary signal pressure. Accordingly, since the opening amount of the optional device spool 4 is controlled by the secondary signal pressure that passes through the electro proportional pressure reducing valve 10 to limit the amount of hydraulic fluid that is supplied to the optional device, the movement of the attachment can be prevented from being limited.
However, as illustrated in FIG. 3, in the case where a separate input signal algorithm or device, which can set the extent of the preference in accordance with the load conditions of the optional device or the operation amount of the attachment, is not provided, the movement of the specific attachment may be limited due to the load pressure that is generated in the optional device.